The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
The propulsion units for aircrafts generally include a nacelle forming a generally circular outer envelope, comprising inside a turbojet engine arranged along the longitudinal axis of this nacelle.
The turbojet engine receives the fresh air coming from the upstream side, or the front side, and rejects from the downstream side, or rear side, the hot gases coming from the combustion of fuel, which give a certain thrust.
The turbofan engines have around the motor fan blades generating a significant secondary cold air flow along an annular flow path passing between this motor and the nacelle, which adds a high thrust during normal operation providing a direct jet.
Some nacelles include a thrust reverser system which closes at least partially the annular cold air flow path, and rejects the secondary flow forwards while forming a reverse jet which generates a braking counter-thrust of the aircraft.
A known type of nacelle, presented particularly by the document FR-A1-2920144, includes two half-cowls covering the middle section surrounding the secondary flow fan, called hereinafter cowls, including a hinge having a longitudinal axis located at the upper portion, so as to allow an opening of these cowls for maintenance operations.
To guarantee the structural strength of the two cowls, a locking device is known, which includes a telescopic connecting rod, the connecting rod comprising a rod which is slidably mounted along a generally transverse axis, in a tubular element, between a retracted position corresponding to a closed cowls configuration and a deployed position corresponding to an open cowls configuration.
The movable rod of the connecting rod has a distal end which is linked on the first cowl, and a proximal end which is adapted to be linked on the second cowl via a locking means.
The locking means is designed to interlock the cowls in their closed position, by blocking the movable rod of the connecting rod.
Furthermore, the locking device includes an assembly allowing linking the connecting rod on a fixed portion of the propulsion unit, for example on the mast of the aircraft or on the motor, this assembly comprising a bracket, a vertical rod and a yoke joint.
The bracket is fastened on the mast, or on the motor, and the vertical rod is mounted in a pendulating manner on the bracket about a longitudinal pivot axis.
The yoke joint is slidably mounted vertically and pivoting on the vertical rod, about a vertical axis perpendicular to the sliding axis of the connecting rod.
In addition, the yoke joint is pivotally mounted on the connecting rod about a longitudinal axis, perpendicular to the sliding axis of the connecting rod.
To ensure maintenance of the support function of the connecting rod and the yoke joint, the vertical rod is equipped with a stop which allows supporting the yoke joint which is driven downwardly in the open cowls configuration.
Upon closing the cowls, the connecting rod is engaged in the locking system via ramps which recenter the connecting rod vertically.
Also, to stabilize the locking device in flight, the locking device includes a spring which is interposed axially between the free end of the movable rod of the connecting rod and the tubular element of the connecting rod.
A disadvantage of this type of locking device is that the connecting rod is linked, in the flight phase, both to the movable cowls, by both ends of the sliding rod of the connecting rod, and to the motor, or to the mast, by means of the yoke joint and the bracket.
The cowls, the motor and the mast have different frequencies and vibration levels, so that the connecting rod and the locking means are subjected to severe vibration environment which may reduce the longevity of the locking device.
Furthermore, this type of locking device is hardly adapted to a configuration in which the yoke joint must be fastened on the motor, which may be the case when the mast is too far from the locking means or is not accessible because hidden by the equipment.
Indeed, the motor is arranged under the locking means, while the mast is arranged above the locking means, so that the vertical rod, which is pivotally mounted on the yoke joint, will tend to naturally pivot forwards or backwards under the effect of gravity.
To limit the tilting of the vertical rod, the addition of angular stops will be necessary, these stops must allow keeping a freedom of displacement of the yoke joint along to longitudinal axis relative to the connecting rod during the flight phases.
The position of the connecting rod in the open cowls configuration will be uncertain, which will call for providing more substantial recentering ramps to ensure the engagement of the connecting rod with the locking means upon closing the cowls.